Consultation-liaison psychiatry started in the 1930s when the deinstitutionalisation process allowed the development of new types of psychiatric interventions in primary care and general hospitals. Consultation-liaison is an operational model defined by the environmental and institutional context of practice. It developed progressively as a sub-specialty of psychiatry and gained its own specificity in terms of clinical practice, organisation of care, training and research. More recently and following a similar process, old age psychiatry has developed as another subspecialty in psychiatry, with a scope based on the targeted population of older individuals. Consultation-liaison in old age psychiatry consequently emerged from this double development of consultation-liaison psychiatry and old age psychiatry.